Generally, thermal actuated printheads use resistive elements or the like to achieve ink expulsion. A representative thermal inkjet printhead has a plurality of thin film resistors provided on a semiconductor substrate. A top layer defines firing chambers about each of the resistors. Propagation of a current or a “fire signal” through the resistor causes ink in the corresponding firing chamber to be heated and expelled through the corresponding nozzle.
To form the resistors, a resistive material is deposited over an insulated substrate, and a conductive material is deposited over the resistive material. The conductive material is photomasked and wet etched to form conductor traces and a beveled surface adjacent a resistor. However, due to the difficultly in controlling the wet etching process, substantially inconsistent resistor lengths (gap in the conductor line) and beveled angles result. A dry etch is generally not used to etch the conductor traces because dry etch selectivity of typical conductor to resistor materials is poor.
The resistive material is photomasked and etched to form resistors. A passivation layer is deposited over the conductor traces. The passivation layer is often susceptible to pinhole defects, and wet chemistry, including those used in subsequent wet processing and inks, may travel through the defects in the passivation layer to the conductor layer. The conductor layer thereby begins to corrode.